Extended, or embedded, wafer-level ball grid array (eWLB) packages are used to extend the size of a WLB package beyond the area of the integrated circuit (IC) die in order to provide it with a higher ball count and greater fan out for making electrical interconnections between the pads of the IC die and external electrical circuitry. After the IC dies have been fabricated on a semiconductor wafer, they are singulated into individual dies. The individual dies are then reconstituted on an artificial wafer, which typically comprises a piece of tape on which the dies are positioned front face down and a polymer molding material that encapsulates the dies. It should be noted that the dies that are reconstituted on the artificial wafer may be the same types of dies that were singulated from the same wafer or they may be different types of dies that were singulated from different types of wafers.
After the polymer molding material has been cured to form a mold about the dies, the tape is removed to expose the front side of the wafer, which is the side of the artificial wafer that is co-planar with the front faces of the dies. Wafer-level processes are then used to deposit and pattern layers of dielectric material and metal on the front side of the artificial wafer to form conductive traces. First ends of the conductive traces are in contact with the pads of the dies. Second ends of the conductive traces fan out away from the respective dies. Solder balls are then deposited at particular locations on the front side of the artificial wafer in contact with the second ends of the conductive traces, thereby establishing electrical interconnections between the solder balls and the pads of the respective dies. The artificial wafer is then sawed to singulate the individual eWLB packages from one another. Each singulated eWLB package contains at least one die, but may contain more than one die. In cases where the eWLB package contains more than one die, the dies may of the same type or different types.
After the eWLB packages have been singulated, an eWLB package is typically mounted on a printed circuit board (PCBs) on which other IC packages and/or other electrical components are also mounted. The eWLB package is placed on the PCB such that the solder balls of the eWLB package are in contact with electrical contacts of the PCB. The side of the eWLB package on which the solder balls are disposed is typically referred to as the front side of the package, whereas the opposite side of the eWLB package is typically referred to as the rear side of the package. A solder reflow process is then performed to permanently bond the solder balls of the eWLB package to the respective electrical contacts of the PCB. In this way, the pads of the die(s) of the eWLB package are electrically interconnected with the electrical contacts of the PCB.
In eWLB packages, any electrical wiring that needs to be made inside of the mold is made from the front side of the eWLB package. In some cases, however, electrical contact pads of the die are located on the rear face of the die, or on both the front and rear faces of the die. For example, most optoelectronic dies such as light emitting diode (LED) dies, photodiode dies and vertical cavity surface emitting laser diode (VCSEL) dies have electrical contact pads on their front and rear faces. Forming the electrical wiring that is needed to make the electrical interconnections between the solder balls of the eWLB package and electrical contact pads located inside of the mold on the rear faces of the dies can be difficult due to the fact that these contact pads are inside of the mold.
A variety of solutions to this problem have been proposed, some of which are disclosed in U.S. Pat. No. 7,048,450, which is assigned to the assignee of the present application and which is incorporated herein by reference. Such solutions typically involve creating a thru-mold via (TMV) that extends from the front side of the eWLB package to the rear side of the package and then connecting the TMV to the contact pad(s) disposed on the rear face of the die with a bond wire or a metal bridge. While such solutions work satisfactorily, they are relatively difficult to implement. Also, the use of bond wires and the like is inconsistent with one of the benefits of eWLB technology, which is that it avoids the use of bond wires and uses wafer-level processes to form the interconnections between the solder balls and the contact pads of the die.
A need exists for an eWLB package and method that allow electrical connections to be more easily made to the rear faces of the dies.